The materials, each consisting of two or more positively charged metal ions and oxygen, are used in a wide range of applications including fast ion conductors in solid oxide fuel cells, host materials for nuclear waste containment, and thermal barrier coatings for gas turbine jet engines.

For their study, the team used state-of-the-art neutron characterization techniques to gain a detailed understanding and new insights into the nature of the atomic motifs in these materials. The work was published in the journal Nature Materials on Feb. 29.

“The complex oxides we analyzed in this study — pyrochlore and spinel — have been investigated for decades by different researchers,” says Lang. “When subjected to extreme environments such as high temperatures or high-energy radiation, many of these compounds partially lose their long-range crystal structure, and the multiple cations were thought to randomly exchange crystal sites.”

Lang said the multidisciplinary research team and the unique capabilities of ORNL’s Spallation Neutron Source, a DOE Office of Science User Facility, helped the team discover a novel atomic disordering mechanism in these materials.

With the help of SNS instrument scientists Mikhail Feygenson and Joerg Neuefeind, Lang and his team used the Nanoscale-Ordered Materials Diffractometer (NOMAD) for an in-depth look at the local crystal structure of their samples — a NOMAD first for neutron scattering experiments on ion-irradiated materials.

Neutrons are indispensable for this type of study because they can accurately detect the position of oxygen atoms present in materials.

“Using neutrons to measure samples of such small sizes would have been difficult, if not impossible, just a few years ago,” says Feygenson. “However, with the combination of the high neutron flux of SNS and the wide detector coverage of the NOMAD instrument, scientists can look at very small samples, which are typically the domain of X-ray scattering experiments.”